Project Summary Bacteria use energy dependent proteases to respond to stressful conditions. These proteases serve a dual role: destroying aberrant, potentially toxic, damaged proteins and generating stress responsive signals through degradation of regulatory factors. Cells often arrest replication in response to stress, but how regulated prote- olysis contributes to cell cycle arrest in bacteria is currently poorly understood. This proposal addresses how stress related proteases target replication factors using a combination of biochemical, genetic and proteomic approaches, specifically focusing on proteases and replication factors from the model bacteria Caulobacter crescentus. Aims 1 and 2 determine how misfolded proteins generated during proteotoxic stress directly stimu- late the Lon protease to destroy the replication initiator DnaA and cause growth arrest during stress. Aims 3 and 4 focus on how partial processing of the clamp loader subunit DnaX by the ClpXP protease is critical for replication stress tolerance during DNA damage. Because these proteases and replication factors are highly conserved throughout all bacteria, these results will impact our general understanding of replication, proteoly- sis, and stress tolerance. The critical role of these proteases in bacterial virulence and pathogenicity, together with the universal requirement for these proteases in bacterial stress responses, suggests that they are excel- lent targets for development of new antibiotic strategies that are of immediate human health need.